The Erlang distribution Random Number Generator (RNG) that allows stream numbers to be set deterministically. More...

#include "random-variable-stream.h"

Inheritance diagram for ns3::ErlangRandomVariable:

Collaboration diagram for ns3::ErlangRandomVariable:

Public Member Functions
	ErlangRandomVariable ()
	Creates an Erlang distribution RNG with the default values for k and lambda.

virtual uint32_t	GetInteger ()
	Get the next random value drawn from the distribution.

uint32_t	GetInteger (uint32_t k, uint32_t lambda)
	Get the next random value drawn from the distribution.

uint32_t	GetK () const
	Returns the k value for the Erlang distribution returned by this RNG stream.

double	GetLambda () const
	Returns the lambda value for the Erlang distribution returned by this RNG stream.

double	GetValue () override
	Get the next random value drawn from the distribution.

double	GetValue (uint32_t k, double lambda)
	Get the next random value drawn from the distribution.

Public Member Functions inherited from ns3::RandomVariableStream
	RandomVariableStream ()
	Default constructor.

	RandomVariableStream (const RandomVariableStream &)=delete

	~RandomVariableStream () override
	Destructor.

int64_t	GetStream () const
	Returns the stream number for the RngStream.

bool	IsAntithetic () const
	Check if antithetic values will be generated.

RandomVariableStream &	operator= (const RandomVariableStream &)=delete

void	SetAntithetic (bool isAntithetic)
	Specify whether antithetic values should be generated.

void	SetStream (int64_t stream)
	Specifies the stream number for the RngStream.

Public Member Functions inherited from ns3::Object
	Object ()
	Constructor.

	~Object () override
	Destructor.

void	AggregateObject (Ptr< Object > other)
	Aggregate two Objects together.

void	Dispose ()
	Dispose of this Object.

AggregateIterator	GetAggregateIterator () const
	Get an iterator to the Objects aggregated to this one.

TypeId	GetInstanceTypeId () const override
	Get the most derived TypeId for this Object.

template<typename T >
Ptr< T >	GetObject () const
	Get a pointer to the requested aggregated Object.

template<>
Ptr< Object >	GetObject () const
	Specialization of () for objects of type ns3::Object.

template<typename T >
Ptr< T >	GetObject (TypeId tid) const
	Get a pointer to the requested aggregated Object by TypeId.

template<>
Ptr< Object >	GetObject (TypeId tid) const
	Specialization of (TypeId tid) for objects of type ns3::Object.

void	Initialize ()
	Invoke DoInitialize on all Objects aggregated to this one.

bool	IsInitialized () const
	Check if the object has been initialized.

void	UnidirectionalAggregateObject (Ptr< Object > other)
	Aggregate an Object to another Object.

Public Member Functions inherited from ns3::SimpleRefCount< Object, ObjectBase, ObjectDeleter >
	SimpleRefCount ()
	Default constructor.

	SimpleRefCount (const SimpleRefCount &o)
	Copy constructor.

uint32_t	GetReferenceCount () const
	Get the reference count of the object.

SimpleRefCount &	operator= (const SimpleRefCount &o)
	Assignment operator.

void	Ref () const
	Increment the reference count.

void	Unref () const
	Decrement the reference count.

Public Member Functions inherited from ns3::ObjectBase
virtual	~ObjectBase ()
	Virtual destructor.

void	GetAttribute (std::string name, AttributeValue &value, bool permissive=false) const
	Get the value of an attribute, raising fatal errors if unsuccessful.

bool	GetAttributeFailSafe (std::string name, AttributeValue &value) const
	Get the value of an attribute without raising errors.

void	SetAttribute (std::string name, const AttributeValue &value)
	Set a single attribute, raising fatal errors if unsuccessful.

bool	SetAttributeFailSafe (std::string name, const AttributeValue &value)
	Set a single attribute without raising errors.

bool	TraceConnect (std::string name, std::string context, const CallbackBase &cb)
	Connect a TraceSource to a Callback with a context.

bool	TraceConnectWithoutContext (std::string name, const CallbackBase &cb)
	Connect a TraceSource to a Callback without a context.

bool	TraceDisconnect (std::string name, std::string context, const CallbackBase &cb)
	Disconnect from a TraceSource a Callback previously connected with a context.

bool	TraceDisconnectWithoutContext (std::string name, const CallbackBase &cb)
	Disconnect from a TraceSource a Callback previously connected without a context.

Static Public Member Functions
static TypeId	GetTypeId ()
	Register this type.

Static Public Member Functions inherited from ns3::RandomVariableStream
static TypeId	GetTypeId ()
	Register this type.

Static Public Member Functions inherited from ns3::Object
static TypeId	GetTypeId ()
	Register this type.

Static Public Member Functions inherited from ns3::ObjectBase
static TypeId	GetTypeId ()
	Get the type ID.

Private Member Functions
double	GetExponentialValue (double mean, double bound)
	Returns a random double from an exponential distribution with the specified mean and upper bound.

Private Attributes
uint32_t	m_k
	The k value for the Erlang distribution returned by this RNG stream.

double	m_lambda
	The lambda value for the Erlang distribution returned by this RNG stream.

Additional Inherited Members
Protected Member Functions inherited from ns3::RandomVariableStream
RngStream *	Peek () const
	Get the pointer to the underlying RngStream.

Protected Member Functions inherited from ns3::Object
	Object (const Object &o)
	Copy an Object.

virtual void	DoDispose ()
	Destructor implementation.

virtual void	DoInitialize ()
	Initialize() implementation.

virtual void	NotifyNewAggregate ()
	Notify all Objects aggregated to this one of a new Object being aggregated.

Protected Member Functions inherited from ns3::ObjectBase
void	ConstructSelf (const AttributeConstructionList &attributes)
	Complete construction of ObjectBase; invoked by derived classes.

virtual void	NotifyConstructionCompleted ()
	Notifier called once the ObjectBase is fully constructed.

Related Symbols inherited from ns3::ObjectBase
static TypeId	GetObjectIid ()
	Ensure the TypeId for ObjectBase gets fully configured to anchor the inheritance tree properly.

Detailed Description

The Erlang distribution Random Number Generator (RNG) that allows stream numbers to be set deterministically.

This class supports the creation of objects that return random numbers from a fixed Erlang distribution. It also supports the generation of single random numbers from various Erlang distributions.

The Erlang distribution is a special case of the Gamma distribution where $k = \alpha > 0$ is a positive definite integer. Erlang distributed variables can be generated using a much faster algorithm than Gamma variables.

The probability distribution is defined in terms two parameters, the K or shape parameter $\in {1,2 \dots}$ , and the Lambda or scale parameter $\in (0,1]$ . (Note the Wikipedia entry for the Erlang Distribution uses the parameters $(k, \lambda)$ or $(k, \beta)$ . The parameters used here $(k, \lambda)_{\mbox{ns-3}}$ correspond to $(k, \frac{1}{\lambda} = \beta)_{\mbox{Wikipedia}}$ .)

The probability density function is:

$P(x; k, \lambda) dx = \lambda^k \\ \frac{x^{k-1} e^{-\frac{x}{\lambda}}}{(k-1)!} dx, \\ \quad x \in [0, +\infty)$

with mean $\mu = k \lambda$ and variance $\sigma^2 = k \lambda^2$ .

The Erlang RNG value is generated by

$x = - \lambda \sum_{i = 1}^{k}{\ln u_i}$

where the are uniform random variables on [0,1).

Example

Here is an example of how to use this class:

uint32_t k = 5;
double lambda = 2.0;
 
Ptr<ErlangRandomVariable> x = CreateObject<ErlangRandomVariable> ();
x->SetAttribute ("K", IntegerValue (k));
x->SetAttribute ("Lambda", DoubleValue (lambda));
 
double value = x->GetValue ();